1. Field of the Invention
The present invention relates to a process and an apparatus for taking up, or measuring, an object space using an opto-electronic range finder which operates according to a method of determining the time-of-flight of a signal. In the context of the present specification, the term “determining the time-of-flight” should be understood in its broadest meaning, i.e. encompassing both counting the time between the emission of a transmitter signal up to the receipt of a reflected signal and, in the case of a continuous-wave laser, determining the time-of flight by determining the phase shift between the transmitted beam and the reflected beam received.
More specifically the present invention relates to such a process which comprises a first take-up step in which optical transmitter signals in form of a beam of a predetermined first divergence angle are transmitted along a first path of rays into the object space, and after reflection of such an optical signal from an object it is received by a receiver, i.e. after a time-of flight of said transmitter signals and said reflected signals which, thus, have a certain time relationship during a measuring cycle between a transmitted and a reflected signal.
While appropriate optics are assigned to the transmitter and the receiver and define a first and second optical axis, an evaluating step determines the distance of the above mentioned object in the object space from the time-of-flight meant in the above sense. To obtain different distance values even from larger objects, a scanning step by deviating the direction of the first and second optical axes by a certain angle of deflection between two subsequent measuring cycles. Since the scanning step is effected over a certain maximum deviation angle of a scanner, it is contemplated to decode this angle in any position of the scanner for determining the actual angle of deviation during scanning.
When an object space has to be taken up, reference marks, e.g. retro-reflectors, are arranged in the object space which have either defined geographical coordinates, thus being adapted to define a coordinate system (as soon as their position in relation to the “image” taken up is known) into which the image can be inserted in correspondence with reality, or to form a 3-D image of the object space by taking the object space from at least two different directions, and using said coordinates to form a 3-D image, e.g. by known CAD-computer software. The term “image” in the context of range finding means that all the measuring results during scanning result in a so-called point cloud which is often called “distance image”. However, it already been suggested to superimpose such a “distance image” by a two-dimensional image of the object scene, and in this case all ingredients necessary to form a 3-D image are present, i.e. a two-dimensional image plus the depth of the scene derived from the distance measurings which form the third dimension.
The invention relates also to an apparatus for carrying out the above described process.
2. Background Information
Since retro-reflectors, generally used as reference marks, have typically a size of about 25 mm×25 mm up to 100 mm×100 mm and modem range finders, at a beam divergence smaller than 1 mrad, e.g. 0.3 mrad, have a radius of action significantly larger than 1000 m, one cannot ensure that the range finder detects all reference marks. This may result in problems, particularly in the case of a measuring program which runs, to a high degree, automatically, and may result in the necessity to repeat measurements. Since the evaluation, particularly combining of a plurality of detail images and the assigned data files to obtain a 3-D model is, in general, made off-line and not in the field, this may lead to a considerable expenditure.